Seven babies at a California daycare center were swaddled so tightly at naptime that they could barely breathe, say police, resulting in the arrests of the center's director and her sister, an employee.

Authorities were tipped off to the swaddling practice at Universal Preschool in Livermore by a 19-year-old former employee who reportedly "quit in disgust" after witnessing children being restrained improperly,

Swaddling a child is a common practice for babies up to 6 months of age; however, older children are swaddled only if advised by the parent, said authorities, and the seven babies at Universal Preschool were between 7 and 11 months of age.

Arrested on Wednesday were Universal Preschool's director Lida Sharaf, 33, and her sister Nazila Sharaf, 35. They were charged with three counts of felony child neglect and abuse and four counts of misdemeanor child neglect and abuse, reported the San Francisco Chronicle. They were being held in lieu of $700,000 bail.

An investigation concluded that the sisters had wrapped three boys and four girls in blankets so tightly that their breathing and movement was restricted during naptimes, Officer Steve Goard told the Chronicle, adding that three of the swaddled children suffered from upper-respiratory conditions, which the sisters were aware of.

Police said that children also had their faces covered by blankets.

The investigation also found numerous other violations, including an infant sleeping in a high chair, a worker without a proper background check, and more children than the school was licensed to care for, reported local ABC News affiliate KGO-TV.

Seven babies at a California daycare center were swaddled so tightly at naptime that they could barely breathe, say police, resulting in the arrests of the center's director and her sister, an employee.